The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

4. Survey of Novel Multiphoton Active Materials 1257 4.1. Multiphoton Absorbing Systems 1257 4.2. Organic Molecules 1257 4.3. Organic Liquids and Liquid Crystals 1259 4.4. Conjugated Polymers 1259 4.4.1. Polydiacetylenes 1261 4.4.2. Polyphenylenevinylenes (PPVs) 1261 4.4.3. Polythiophenes 1263 4.4.4. Other Conjugated Polymers 1265 4.4.5. Dendrimers 1265 4.4.6. Hyperbranched Polymers 1267 4.5. Fullerenes 1267 4.6. Coordination and Organometallic Compounds 1271 4.6.1. Metal Dithiolenes 1271 4.6.2. Pyridine-Based Multidentate Ligands 1272 4.6.3. Other Transition-Metal Complexes 1273 4.6.4. Lanthanide Complexes 1275 4.6.5. Ferrocene Derivatives 1275 4.6.6. Alkynylruthenium Complexes 1279 4.6.7. Platinum Acetylides 1279 4.7. Porphyrins and Metallophophyrins 1279 4.8. Nanoparticles 1281 4.9. Biomolecules and Derivatives 1282 5. Nonlinear Optical Characterizations of Multiphoton Active Materials 1282

Multiphoton Absorbing Materials : Molecular Designs, Characterizations, and Applications

Nanoscale systems are forecast to be a means of integrating desirable attributes of molecular and bulk regimes into easily processed materials. Notable examples include plastic light-emitting devices and organic solar cells, the operation of which hinge on the formation of electronic excited states, excitons, in complex nanostructured materials. The spectroscopy of nanoscale materials reveals details of their collective excited states, characterized by atoms or molecules working together to capture and redistribute excitation. What is special about excitons in nanometre-sized materials? Here we present a cross-disciplinary review of the essential characteristics of excitons in nanoscience. Topics covered include confinement effects, localization versus delocalization, exciton binding energy, exchange interactions and exciton fine structure, exciton-vibration coupling and dynamics of excitons. Important examples are presented in a commentary that overviews the present understanding of excitons in quantum dots, conjugated polymers, carbon nanotubes and photosynthetic light-harvesting antenna complexes.

Excitons in nanoscale systems

Nanocrystals or quantum dots of the IV−VI semiconductors PbS, PbSe, and PbTe provide unique properties for investigating the effects of strong confinement on electrons and phonons. The degree of confinement of charge carriers can be many times stronger than in most II−VI and III−V semiconductors, and lead salt nanostructures may be the only materials in which the electronic energies are determined primarily by quantum confinement. This Account briefly reviews recent research on lead salt quantum dots.

Lead Salt Quantum Dots: the Limit of Strong Quantum Confinement

Polymer composites are one of the most attractive near-term means to exploit the unique properties of carbon nanotubes and graphene. This is particularly true for composites aimed at electronics and photonics, where a number of promising applications have already been demonstrated. One such example is nanotube-based saturable absorbers. These can be used as all-optical switches, optical amplifier noise suppressors, or mode-lockers to generate ultrashort laser pulses. Here, we review various aspects of fabrication, characterization, device implementation and operation of nanotube-polymer composites to be used in photonic applications. We also summarize recent results on graphene-based saturable absorbers for ultrafast lasers.

Nanotube–Polymer Composites for Ultrafast Photonics

We observe that the temperature coefficients of electron-hole pair energies $(dE/dT)$ in PbS and PbSe quantum dots depend strongly on the size of the quantum dot. With decreasing size the temperature coefficient of the lowest electron-hole pair energy ${\mathrm{dE}}_{g}/dT$ decreases by more than an order of magnitude from the bulk value. The weak temperature dependence found in the strong-confinement limit is expected for atomiclike levels, but has not been observed previously in a semiconductor.

Size-Dependent Temperature Variation of the Energy Gap in Lead-Salt Quantum Dots

The controlled synthesis of PbSe nanocrystal quantum dots with narrow size distributions was achieved through phase decomposition of the PbSe solid solution in a phosphate glass host. Structural characterization by electron microscopy and x-ray diffraction shows that the dots have mean diameters between 2 and 15 nm. The exciton Bohr radius aB=46 nm in PbSe, so these quantum dots provide unusual and perhaps unique access to the regime of strong quantum confinement. The optical absorption spectra are compared to the predictions of a theoretical treatment of the electronic structure. The theory agrees well with experiment for dots larger than ∼7 nm, but for smaller dots there is some deviation from the theoretical predictions.

http://staff.chess.cornell.edu/~shen/Articles_published/APL97_PbSe.pdf

Synthesis and characterization of PbSe quantum dots in phosphate glass

Soda lime glasses polarized either with an open or a blocking anode have been characterized by IR reflectance spectroscopy and a combined analysis of second harmonic generation and Raman imaging. The experimental results clearly show that the electrode nature influences strongly (i) the thickness of the space charge layer, (ii) the χ(2) efficiency, and (iii) the structural rearrangements. Besides, using theoretical models accounting for charge carriers’ mobilities, the respective influence of two distinct compensation mechanisms, that is an injection of positive charges (H3O+/H+ ions) or a drift of oxygen ions, have been confirmed.

How Does Thermal Poling Affect the Structure of Soda-Lime Glass?

We studied a femtosecond laser shaping of silver nanoparticles embedded in soda-lime glass. Comparing experimental absorption spectra with the modeling based on Maxwell Garnett approximation modified for spheroidal inclusions, we obtained the mean aspect ratio of the re-shaped silver nanoparticles as a function of the laser fluence. We demonstrated that under our experimental conditions the spherical shape of silver nanoparticles changed to a prolate spheroid with the aspect ratio as high as 3.5 at the laser fluence of 0.6 J/cm2. The developed approach can be employed to control the anisotropy of the glass-metal composites.

/pdf/correction-corrigendum-revealing-the-nanoparticles-aspect-3436t1x71e.pdf

Correction: Corrigendum: Revealing the nanoparticles aspect ratio in the glass-metal nanocomposites irradiated with femtosecond laser

Optical-absorption spectra of PbSe and PbS spherical quantum dots have been studied both theoretically and experimentally. Exact theoretical analysis of the energy spectra and optical transitions has been carried out in the framework of four-band $\mathbf{k}\ensuremath{\cdot}\mathbf{p}$-method with full account of the anisotropy effects. It is demonstrated that strong anisotropy of the energy bands of bulk PbSe and PbS results in pronounced optical transitions in quantum dots, which are forbidden in isotropic approximation. These anisotropy-induced transitions have been clearly observed in the measured absorption spectra of the PbSe and PbS quantum dots.

Andrey A. Lipovskii

Papers

Size-Dependent Temperature Variation of the Energy Gap in Lead-Salt Quantum Dots

Synthesis and characterization of PbSe quantum dots in phosphate glass

How Does Thermal Poling Affect the Structure of Soda-Lime Glass?

Correction: Corrigendum: Revealing the nanoparticles aspect ratio in the glass-metal nanocomposites irradiated with femtosecond laser

Anisotropy-induced optical transitions in PbSe and PbS spherical quantum dots